The present invention is generally directed to donor rolls and more specifically, the present invention is directed to donor rolls made from a graphite loaded phenolic resin. The donor rolls of the present invention are useful in a number of imaging processes including electrostatographic imaging systems.
The development of images by various methods, including electrostatographic means, is well known. In several of these methods, toner particles are deposited on an electrostatic latent image present on an insulating surface, such as selenium, utilizing, for example, cascade development, magnetic brush development, powder cloud development, and touchdown development. In view of several disadvantages associated with two-component systems, considerable effort has been directed to designing processes which utilize toner particles only.
In many of the single component development processes, conductive toner particles are selected, and imagewise toner deposition onto the photoconductive member is obtained by induction charging of the toner particles. Electrostatic transfer of conductive toner particles to plain bond paper is, however, usually inefficient as the charge on the toner particles can be reversed by induction charging from the paper during the transfer step. Accordingly, electrophotographic systems wherein conductive single component toner particles are used can require a special overcoated insulating paper to achieve sufficient electrostatic toner transfer. Furthermore, in single component processes with conductive toner particles the control of undesirable background, or background suppression, cannot usually be achieved with electrostatic forces as the toner particles are inductively charged, and deposited on the image bearing member, which is not the situation with two-component developer processes where control of background development is accomplished by electrostatic forces acting on the triboelectrically charged toner particles, causing these particles to be directed away from image bearing members.
Recently, there has been disclosed an efficient, single component, economical, simple process, and apparatus for the development of latent electrostatic images wherein insulative, nonmagnetic, or color toner particles are appropriately charged; and there is obtained two-component image quality utilizing a single component development apparatus. In this system, as detailed hereinafter, and as described in U.S. Pat. No. 4,459,009, there is selected a charging roll means which simultaneously meters and charges toner particles. A donor electrode serves to transport the toner particles, which electrode can be comprised of numerous suitable materials, including for example, aluminized Mylar overcoated with a polymer containing carbon black, electroformed nickel, or a carbon black loaded extruded polymer. While these materials may be satisfactory for their intended purposes, there continues to be a need for a donor roll with improved characteristics for applying toner to the charged photoreceptor.
Furthermore, known prior art donor rolls such as Krylon, available from Borden, Inc., coated onto a nickel substrate, although suitable for their intended purposes are not scratch resistant over extended time periods. Thus, these coatings permit scratches to form on the toner transporting means, which in turn adversely affects image copy quality. Additionally, toner particles appear to permanently adhere to the surface of transporting members with Krylon coatings which adhesion results in undesirable high background deposits on the resulting developed images.
It is also known to form a developing member incorporating a dielectric material in which conductive particles are dispersed. As described in U.S. Pat. No. 4,990,963 to Yamamoto et al., developing rollers are known which are formed by pouring or spraying a solvent/resin/conductive particle solution. The volatile portion of the solution is evaporated leaving a resin/conductive particle substrate for use in a developer roller.